1. Field of the Invention
The present invention relates generally to a rotatable member that is able to achieve a balanced condition throughout a range of rotational speed and, more specifically, a system that dynamically balances a rotatable member through continual determination of out of balance forces and motion and takes corresponding counter balancing action.
2. Description of the Prior Art
Many different types of balancing schemes are known to those skilled in the art. When rotatable objects are not in perfect balance, nonsymmetrical mass distribution creates out-of-balance forces because of the centrifugal forces that result from rotation of the object. Although rotatable objects find use in many different applications, one particular application is a rotating drum of a washing machine.
U.S. Pat. No. 3,304,032, which issued to Yapes on Feb. 14, 1967, discloses a self-balancing support mechanism that includes a cabinet designed to receive a washing machine. One side of the cabinet is provided with a strap member which extends across the lower end of the cabinet and includes a pair of space upwardly diverging slots. The invention also provides a mounting leg for operative attachment of the strap. The mounting leg includes an elongated, generally horizontal central portion with one of a pair of downwardly extending support feet formed at each end thereof. The mounting leg includes a pair of spaced threaded holes and an attachment stud is securely threaded into each of these holes and extends through a cooperating one of the slots. When the machine is mounted on a base surface, the weight of the machine causes the studs to slide within the slots until the machine assumes a position in which the weight distribution among the various support contact members or feet is balanced.
U.S. Pat. No. 3,275,146, which issued to Severance et al on Sep. 27, 1966, describes a laundry machine with an improved balancing mechanism. It relates to washers and dryers of the horizontal axis drum type in which it is desirable to have the rotatable cylinder rotate at a speed as high as practicable during extraction of liquid from clothing. As is well known, any unbalanced condition in the load within the drum causes serious vibration conditions. The mechanism provides application control means that are operatively connected between the rotatable drum mounting means and the support means of the machine including a relatively thin leaf spring member which is alternately placed in tension and compression to control water balancing and clutch control functions. The device described in U.S. Pat. No. 3,275,146 is an improvement of the means for overcoming imbalance and vibration that are disclosed in U.S. Pat. No. 3,151,067.
U.S. Pat. No. 3,149,502, which issued to Caruso et al on Sep. 22, 1964, discloses an automatic balancing apparatus. The invention relates to an apparatus for continuously balancing a rotor while the rotor is rotating. It provides means to produce a signal that is indicative of the dynamic unbalance of the rotor while rotating. Electrically responsive balancing means are positioned on the rotor to vary the dynamic characteristics of the rotor. Means are connected to the signal producing means to energize the electrically responsive balancing means in accordance with signals received from the signal producing means in a manner to thereby vary the dynamic characteristics of the rotor to continuously tend to counterbalance dynamic unbalancing forces in the rotor during rotation. The apparatus comprises several modifications over previous balancing techniques. In one, portions of the rotor are electrically heated to change the dynamic characteristics of the rotor and, when such heating is selectively performed, the dynamic characteristics of the rotor may be changed to continuously tend to counterbalance any dynamic unbalancing forces in the rotor during rotation. Another modification comprises a pair of balancing members positioned on the rotor to be balanced. The balancing members can be dynamically unbalanced by relative movement between the members and, by changing the angular relationship between the two balancing members, the dynamic characteristics of the rotor to be balanced may be varied to continuously counterbalance any dynamic unbalancing forces in the rotor during rotation.
Previous methods for dynamically balancing a rotatable member have experienced severe limitations in the degree of balance that can be achieved and in the rotational speeds under which they are workable. In addition, previous balancing methods have based their operation on certain assumptions that minimize the need for certain sensed parameters, e.g., the support of the equipment being balanced is rigid and rigidly fastened to a significant mass such as a concrete slab. It would therefore be beneficial if a dynamic balancing scheme could be provided which accounts for both forces and motion caused by an imbalance condition of the rotor.